1. Field of the Invention
The present invention relates to a high-density disk structure preventing collision of an optical pickup's objective lens with a high-density disk which is placed upside down in a disk device being able to reproduce and record signals from/to a high-density disk such as a high-density digital versatile disk (called “HD-DVD” hereinafter).
2. Description of the Related Art
A compact disk, usually called “CD,” is 1.2 mm in thickness and 120 mm in diameter as shown in FIG. 1. A CD has a center hole of 15 mm diameter and a clamping zone of 44 mm, which encircles the center hole where the clamping zone is clamped by a damper on a spindle or a turntable installed in a disk device.
When a CD is normally placed into a disk device, its recording layer, which has pit patterns, is approximately 1.2 mm from an objective lens of an optical pickup equipped in the disk device. The objective lens for a CD has a numerical aperture (NA) of 0.45, which is relatively small.
A digital versatile disk, usually called “DVD,” is 1.2 mm in thickness and 120 mm in diameter like a CD as shown in FIG. 2. A DVD also has a center hole of 15 mm diameter and a clamping zone of 44 mm encircling the center hole.
When a DVD is normally placed into a disk device, its recording layer, which has pit patterns, is approximately 0.6 mm from an objective lens of an optical pickup equipped in the disk device. The objective lens for a DVD has a NA of 0.6, which is relatively large.
A HD-DVD, which is currently being commercialized, is 1.2 mm in thickness and 120 mm in diameter, like a CD as shown in FIG. 3. A HD-DVD also has a center hole of 15 mm diameter and a clamping zone of 44 mm encircling the center hole. If a HD-DVD is normally placed into a disk device, there will be a 0.1 mm gap between its recording layer, which also has pit patterns, and an objective lens of an optical pickup for a HD-DVD, which has the largest NA of 0.85. The optical pickup for a HD-DVD uses a laser beam of shorter wavelength than for a CD or a DVD to record or reproduce signals in high density.
Therefore, in comparison with a CD or a DVD, HD-DVD uses an objective lens that is situated closer to the recording layer, that uses a laser beam of shorter wavelength, and that has a greater NA. According to these conditions, it is possible to concentrate a stronger intensity of light on a smaller beam spot formed on the high-density pit patterns of the recording layer of the HD-DVD. Consequently, the transmitting distance of a laser beam of shorter wavelength is shortened, and the variation of the laser beam and its spherical aberration are minimized.
If a HD-DVD 10 is normally placed onto a turntable 11 installed in a disk device as shown in FIG. 4, a conventional servo-controlling operation for a spindle motor 12 by a motor driving unit 13 and a servo controller 15 is conducted to rotate the placed HD-DVD 10 at a constant and high speed. While the HD-DVD 10 is rotating, a focusing-servo operation is conducted to focus a laser beam for an optical pickup 14 exactly onto the recording layer 9. This operation is performed by moving the objective lens OL of the optical pickup 14 in an up and down direction within an operating distance OD. If a laser beam is exactly in focus, then reproduction (or recording) of high-density pit patterns can be accomplished.
However, when the HD-DVD 10 is misplaced onto the turntable 11 by, for example, being placed upside down as shown in FIG. 5, the HD-DVD 10 will still be rotated at a constant and high speed by the combined servo-controlling operation by the spindle motor 12, the motor driving unit 13, and the servo controller 15. However, if the HD-DVD 10 has been placed upside down, the gap between the recording layer 9 and the objective lens OL of the optical pickup 14 is 1.1 mm greater in comparison with a normally-placed HD-DVD.
In this misplacement, a laser beam cannot be focused within the conventional operating distance of the objective lens OL of the pickup 14. Therefore, the servo controller 15 supervising the focusing-servo operation continues to move the objective lens OL upward to the maximum movable distance ‘OD_Max’ until the laser beam is correctly focused. However, in this case, the objective lens OL will collide with the misplaced HD-DVD 10. Consequently, the HD-DVD 10, the objective lens OL, and/or the servo-mechanism would be irreparably damaged.